August 31 , 2016

by Davidow

The non-titanosauriform macronarian Camarasaurus is one of the American public's favorite macronarian sauropods from the Jurassic, being thought of as the most common macronarian from the Morrison Formation. Very few sauropod workers, however, have tackled the alpha-taxonomy of the genus and its various constituent taxonomy since the papers by Ikejiri (2005) and Osborn and Mook (1921). The result has been the tendency to treat Camarasaurus as a genus in numerous phylogenies of Sauropoda (Upchurch et al. 2004; Wilson 2002) without a comprehensive analysis of intrageneric variation of the genus.

In recent abstracts published at the SVP 2013 and 2014 meetings, Mateus and Tschopp (2013) and Tschopp et al. (2014) work to address the question of intraspecific variation in Camarasaurus. The abstract by Mateus and Tschopp (2013) deals with a newly discovered camarasaurid (SMA 0002) that is referred to Cathetosaurus lewisi based on shared characters with BYU 9047 (holotype of C. lewisi). On the other hand, Tschopp et al. (2013) conduct a specimen-level analysis of all Camarasaurus specimens including the type specimens of currently recognized species of the genus (C. grandis, C. lentus, and C. supremus). The phylogenetic results reported by Tschopp et al. (2014) seem to not only reaffirm the distinctness of Cathetosaurus from Camarasaurus, but they also support the validity of the three historical species of the latter genus.

These preliminary results have prompted me to revisit the synonymy of Caulodon with Camarasaurus performed by Osborn and Mook (1921) and followed by subsequent authors. When placing the two nominal species of Caulodon (C. diversidens and C. leptoganus) in synonymy with Camarasaurus supremus, Osborn and Mook noted that AMNH 5768 and AMNH 5769 were similar to the maxillary teeth of a referred specimen of Camarasaurus supremus (AMNH 5761) in being robust and spatulate-shaped, but were hesitant to rule out the possibility of two different sauropods with spatulate teeth from the Morrison Formation. However, they did not compare the holotypes of Caulodon diversidens and C. leptoganus with the teeth of Giraffatitan or USNM 5730 (referred to Brachiosaurus sp. by Carpenter and Tidwell 1998).

Since the monograph by Osborn and Mook, robust spatulate teeth have been described for numerous non-neosauropod and macronarian sauropods, including USNM 5730, Europasaurus, Mamenchisaurus, Turiasaurus, and Jobaria (Carpenter and Tidwell, 1998; Marpmann et al. 2014; Ouyang and He 2002; Royo-Torres and Upchurch 2012; Russell and Zheng 1994; Sereno et al. 1999). Because robust spatulate teeth are no longer considered diagnostic for Camarasaurus supremus or other camarasaurid species and are widely distributed among non-neosauropod and non-titanosauriform sauropods, Caulodon and its nominal species should not be considered synonymous with Camarasaurus supremus and instead must be considered nomina dubia at Eusauropoda indeterminate.

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